JP2009130846A - Color processing method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that the accuracy of reproducibility information declines and an appropriate color separation table can not be prepared by color prediction referring to the color reproducibility information since grid point arrangement corresponding to the patch in a colorant space is equally allocated regardless of the gradation characteristics of colorants when preparing the patch of the colorants to be used when preparing the color reproducibility information of a medium. <P>SOLUTION: The grid point arrangement for which a color space corresponding to the plurality of colorants is divided in a grid shape is optimized according to single color gradation characteristics for each colorant (S802). After generating the patch for the grid points for which the total colorant amount is within a restriction (S803), the number of the patches is reduced according to print restriction information (S806). Then, the patch is printed on the medium to measure the color (S808), the color measurement value of the grid point where the total colorant amount exceeds the restriction is estimated on the basis of the color measurement value (S810) and thus, an appropriate color reproducibility table is prepared. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color processing method and an image forming apparatus for creating color reproduction characteristic information of a medium used when creating a color separation table for separating image data into data for a plurality of color materials.

  In recent years, in an image forming apparatus that visualizes a color image on a recording medium (medium) such as a color printer, the demand for media by a user has increased as the image quality of the formed image has improved. Accordingly, it has become essential to allow high-quality images to be output to any medium, as well as making it possible to use many types of media in one printer.

  In general, in a color print system using a color printer or the like, color separation processing is performed in which color image data to be formed is separated into color materials (ink and toner) corresponding to the color amounts in the apparatus. This color separation processing is performed based on a color separation table created in advance, but the optimum color separation processing varies depending on the type of media. Therefore, it is preferable to prepare a plurality of color separation tables that realize optimal color separation for each of a plurality of types of media.

  However, according to the conventional technique, since the color separation table is manually created, when designing a color separation table for various types of media, the design period has become considerably long. In order to quickly create a color separation table corresponding to various types of media, a technique for automatically generating a color separation table for an arbitrary medium is required.

  Further, in general, in the color separation table, there is a trade-off relationship between each item such as the gradation property is lost even if the color gamut can be expanded depending on the applied color material. Therefore, it is necessary that the automatically generated color separation table can be arbitrarily adjusted by the user.

  In addition, since the generated color separation table may not be effective in color gamut or the gradation may be lost if the light source is changed, it is necessary to create a color separation table for each light source. For example, it is desirable to enable adjustment by the user by using a user interface that visualizes the color separation table corresponding to the light source on the Lab space.

  As described above, when the color separation table corresponding to the medium is automatically generated, it is necessary to optimize the color separation table according to the light source, that is, a tool for the user to arbitrarily adjust the created color separation table ( User interface). In order to create such a user interface, it is necessary to have a color prediction technique that enables simulation of mixed color development characteristics without performing printing / colorimetry of color patches on a medium.

  In the color prediction technology for simulating the color development characteristics of the conventional mixed color material, it is necessary to divide the color material space into a grid pattern and print all the grid points (hereinafter referred to as primary) to measure the color. . However, due to the limitation of the total amount of color material of the media, a primary that cannot be printed appears. A technique has been considered in which a simple linear correction process is performed on such a non-printable primary so that the primary can strictly adhere to the total color material limit (see, for example, Patent Document 1). However, when the primary is linearly corrected according to the total color material amount limitation, the linear relationship with the surrounding primary may be lost, which may cause the color prediction accuracy to deteriorate. Further, when the number of color materials to be used increases, the number of primaries becomes enormous and the printing load increases.

  In the above-described conventional color prediction process, a color reproduction characteristic table that defines the spectral value of each primary for the medium used is referred to. Here, a color reproduction characteristic table referred to in the color prediction process will be described with reference to FIG.

  FIG. 16 is a flowchart showing a process for creating the color reproduction characteristic table.

  First, in step S1601, parameters are input. Here, the parameters are data such as restriction information on the total amount of color material of the medium, the number of grids in the ink space, and step values. Next, in step S1602, after all primaries are generated, a primary that can be printed because the total color material amount is within the total color material amount limit is generated as a patch. In step S1603, the patch generated in step S1602 is printed on the medium for color measurement, and in step S1604, the color measurement result is input.

  In step S1605, the colorimetric value is used to estimate a primary colorimetric value that cannot be printed because the total color material amount is larger than the total color material amount limit. Thereby, the colorimetric value, that is, the spectral value is obtained for all primaries.

By using the color reproduction characteristic table created as described above, color prediction can be performed for an arbitrary point in the color space including the primary. Specifically, when a signal value of a point to be predicted is input, by performing color prediction by a known cellular Neugebauer process based on the colorimetric values of the primaries around the point in the color reproduction characteristic table, The spectrum value of the point can be output.
JP 2003-334934 A

  However, the conventional color reproduction characteristic table creation process has the following problems. That is, when the primary is determined, the color material space is evenly divided in a lattice shape, and the nonlinearity of the color material is not considered. Therefore, particularly for the monochrome gradation characteristics of the color material, the prediction accuracy may deteriorate due to the influence of the nonlinearity. Furthermore, the color gamut prediction becomes uncertain as the prediction accuracy deteriorates. That is, of course, the accuracy of the color separation table created by color prediction also decreases.

  SUMMARY An advantage of some aspects of the invention is that it provides a color processing method and an image forming apparatus having the following characteristics. That is, when creating a patch of a color material used when creating color reproduction characteristic information of media, the grid point arrangement corresponding to the patch in the color material space is optimized according to the tone characteristic of the color material. . Furthermore, the number of patches to be formed is reduced so as not to degrade the color prediction accuracy. Accordingly, the color reproduction characteristic information is appropriately created, and an appropriate color separation table is created by color prediction with reference to the color reproduction characteristic information.

  As a means for achieving the above object, the color processing method of the present invention includes the following steps.

  That is, a color processing method for creating color reproduction characteristic information of a medium used when creating a color separation table for separating image data into data for a plurality of color materials, which corresponds to the plurality of color materials A grid point acquisition step of acquiring grid points obtained by dividing the color space into a grid, and an input step of inputting colorimetric values obtained by printing patches of the grid points on the medium, In the grid point acquisition step, a monochrome gradation characteristic acquisition step for acquiring a monochrome gradation characteristic for each color material for the medium, and an inflection point detection step for detecting an inflection point in the monochrome gradation characteristic; And a lattice point arranging step of arranging one of the lattice points at the inflection point.

  Furthermore, an acquisition step of restriction information for obtaining restriction information of the total color material amount for the medium, a patch generation step of generating a patch for lattice points whose total color material amount is within the restriction indicated by the restriction information, An estimation step of estimating a colorimetric value of a grid point having a total color material amount larger than the limit indicated by the restriction information based on the colorimetric value input in the input step.

  And a patch number limit obtaining step for obtaining patch number limit information, and a reduction step for reducing the number of patches generated in the patch generation step based on the patch number limit information. To do.

  According to the present invention having the above configuration, a color processing method and an image forming apparatus having the following characteristics can be provided. That is, when creating a patch of a color material used when creating color reproduction characteristic information of media, the grid point arrangement corresponding to the patch in the color material space is optimized according to the tone characteristic of the color material. be able to. Furthermore, the number of patches to be formed can be reduced so as not to degrade the color prediction accuracy. Thereby, the color reproduction characteristic information can be appropriately created, and an appropriate color separation table can be created by color prediction with reference to the color reproduction characteristic information.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the accompanying drawings. The configurations shown in the following embodiments are merely examples, and the present invention is not limited to the illustrated configurations.

<First Embodiment>
Output Process FIG. 1 is a diagram showing an image output process using a plurality of colors in the color printer of this embodiment. In the figure, reference numeral 101 denotes a color matching processing unit for matching the reproduction characteristics of input RGB data with the color of the printer. Reference numeral 102 denotes an ink color separation processing unit for converting the multivalued R′G′B ′ data output from the color matching processing unit 101 into C′M′Y′K ′, which is the color material color of the printer. is there. A halftone processing unit 103 converts the multivalued C′M′Y′K ′ data output from the ink color separation processing unit 102 into the number of gradations that can be expressed by a printer, and outputs CMYK data. . Reference numeral 105 denotes an ink color separation table unit that provides an ink color separation table that is referred to during the interpolation processing in the ink color separation processing unit 102. An ink color separation table creation unit 104 creates an ink color separation table held in the ink color separation table unit 105. Hereinafter, the ink color separation table is also simply referred to as “color separation table”.

  FIG. 2 is a diagram showing a system configuration in the present embodiment. In the figure, reference numeral 202 denotes a computer that holds input image data, and includes an input unit (not shown) such as a mouse for inputting a user instruction. Reference numeral 201 denotes a monitor for displaying image data held in the computer 202. Reference numeral 203 denotes a printer for color printing image data held in the computer 202. In the process configuration shown in FIG. 1 described above, the ink color separation table creation unit 104 is provided in the computer 202, but the rest is the configuration of the printer 203. Note that all configurations may be provided in the computer 202, and the CMYK data output from the halftone processing unit 103 may be input to the printer 203.

  Here, the printing process in the present embodiment will be described with reference to FIGS. 1 and 2. The image data held in the computer 202 is sent to the printer 203 via a cable or a network (not shown) at the time of printing.

  In the printer 203, the color matching processing unit 101 performs color matching processing on the transmitted RGB image data so as to match the color reproduction characteristics of the monitor 201 used by the user. The R′G′B ′ data after the color matching processing is performed in the printer 203 by interpolation processing based on the color separation table already created and held in the ink color separation table unit 105 in the ink color separation processing unit 102. Separated into ink colors CMYK. The C′M′Y′K ′ multi-valued data after ink color separation is converted into CMYK data, which is the number of gradations that can be reproduced by the printer 203 by the halftone processing unit 103, and then stored on a preset medium. Printed on.

  In FIG. 2, reference numeral 204 denotes a group of media that can be printed by the printer 203 (in this example, five types of media A to E). In this embodiment, a corresponding ink color separation table is prepared for each type of printable media. As described above, by mounting the color separation table corresponding to the media type on the printer 203, ink color separation optimal for the media type is performed. The ink color separation table is generated in advance by the ink color separation table creation unit 104, and the generation method thereof will be described later.

  Reference numeral 205 denotes a colorimeter. When creating the ink color separation table in the present embodiment, a color reproduction characteristic table prepared in advance for each medium is referred to. The colorimeter 205 measures the printed primary patch in order to create this color reproduction characteristic table, and the color measurement result is input to the computer 202.

Ink Color Separation Table FIG. 3 is a diagram showing the configuration of the color separation table held in the ink color separation table unit 105. The color separation table stores data corresponding to lattice points in a cube in the RGB three-dimensional space as table data corresponding to the input data R′G′B ′. If the input R′G′B ′ data is not on the grid of the color separation table, the ink color separation processing unit 102 performs an interpolation process using the neighboring grid point data. There are many interpolation methods such as tetrahedral interpolation and cubic interpolation, but any interpolation method may be used.

  Hereinafter, a basic method for creating an ink color separation table in the ink color separation table creation unit 104 will be described.

  FIG. 4 is a diagram showing a cube on the RGB color space for explaining the method of creating the ink color separation table in this embodiment, and the eight vertices of the cube are respectively W, C, M, Y, and R. , G, B, Bk. And all 19 which connect WC, M, Y, R, G, B-Bk, MR, RY, YG, GC, CB, B-M, and W-Bk. The book line is shown as a thick solid line. When the number of bits of input data in the ink color separation processing unit 102 is 8, the coordinates of each vertex of W, C, M, Y, R, G, B, and Bk are expressed as follows.

    W = (255, 255, 255): White, that is, a media background color.

    C = (0, 255, 255): Indicates a cyan primary color.

    M = (255, 0, 255): Indicates a magenta primary color.

    Y = (255, 255, 0): Indicates a yellow primary color.

    R = (255, 0, 0): Indicates a red primary color.

    G = (0, 255, 0): Indicates a green primary color.

    B = (0, 0, 255): Indicates a blue primary color.

    Bk = (0, 0, 0): Black, that is, the darkest point of the printer.

  In the ink color separation table creation unit 104, first, WC, M, Y, R, G, B-Bk, MR, RY, YG, GC shown by thick solid lines in FIG. , C-B, B-M, and W-Bk are created as table data. Thereafter, all the table data is created by performing an internal interpolation process for the ink colors corresponding to the internal grid points.

  As described above, the printer 203 of the present embodiment can use a plurality of types of media (five types in the example of FIG. 2). However, for the sake of simplicity of explanation, an example using two types of media will be described below. explain. That is, an example is shown in which the printer 203 can use the medium A, which is the first type of media, and the medium B, which is the second type of media, and prepare the respective color separation tables.

  In order to prepare a different color separation table for each media type, it is conceivable to manually create all the media types, that is, manually input table data for each line indicated by a thick solid line in FIG. . However, with such a method, it is not easy to create a color separation table for a plurality of media types. Therefore, in this embodiment, after manually creating a color separation table for a certain media type, color separation tables for other media types are automatically created based on the manually created color separation table. That is, after the color separation table for medium A is manually created, the color separation table for medium B is automatically created based on this.

Color Separation Table Automatic Creation Processing Hereinafter, automatic color separation table creation processing in the ink color separation table creation unit 104 of this embodiment will be described.

  FIG. 5 is a flowchart showing an automatic creation process of the color separation table for the medium B in the ink color separation table creation unit 104.

  First, in step S501, a color separation table for media A is acquired. It is assumed that the color separation table for medium A has already been manually created and held in the ink color separation table unit 105. In step S502, the total color material amount restriction information of the medium B is acquired. Note that the total color material amount restriction information of the medium B may be input by a user from an input unit (not shown), or may be acquired from a table stored in the computer 202 in advance. As a result, the total color material amount that does not cause bleeding or the like in the media B is defined.

  In step S503, in accordance with the total color material amount restriction information of the medium B, the frame line of the color separation table of the medium B is automatically generated so as to comply with the total color material amount restriction. Details of the automatic frame line generation processing will be described later. In step S504, the frame line is optimized by color prediction. Details of the optimization process by color prediction will be described later. In step S505, data of all grid points within the frame of the color separation table of the medium B is generated by internal interpolation. Thereby, the final color separation table of the medium B is completed.

  Note that the total color material amount restriction defined in step S502 may be a value that causes slight blurring or the like, and is not limited to the fact that blurring does not occur at all.

● Automatic frame line generation process for color separation table (Details)
FIG. 6 is a flowchart showing the automatic generation processing of the frame line of the color separation table that strictly observes the total color material amount of the medium B in step S503 of FIG. In this process, the frame line of the color separation table of the medium B is automatically generated based on the frame line of the color separation table of the medium A that has been manually created in advance.

  First, in step S603, various parameters such as the priority order of the evaluation items in the formed image and the nonlinear correction coefficient for nonlinear interpolation are acquired. In step S604, ink colors that can be used by the printer 203 are classified. Here, an example will be shown in which ink colors are classified into three types: main color, light color, and adjacent color. That is, description will be made assuming that the main color is CMYK ink, the light color is light cyan (Lc), light magenta (Lm), dark gray (Lk1), light gray (Lk2), and the adjacent color is RGB ink.

  Next, in step S605, based on the color separation table of medium A, the frame line of the color separation table of medium B is set. With this frame line, W-Bk, WC, M, Y, R, G, B-Bk, MR, RY, Y-G, GC, CB, B-M It is a total of 19 lines to connect. Specifically, Bk and other color switching point information by under color removal (UCR) and separation ratio information of each color material color are acquired from the color separation table of medium A for each frame line.

  Subsequent processing is sequentially performed for each of the 19 frame lines. As the processing order, first, lines connecting the W and Bk points and the color points (C, M, Y, R, G, and B) are used. Process first, then process the line connecting the color points.

  Here, C, M, Y, R, G, B, Bk, and W points on the color space are considered as primary points.

  In step S606, the color separation value of the primary point in the frame line set in step S605 is calculated so as to keep the total color material amount restriction information of the medium B. In step S607, the color separation value of the frame line is interpolated. For example, for the primary point C in the color separation table of the medium B, the total color material amount is set to 180% in the color separation table of the medium A, and the total color material amount in the medium B calculated in step S606 is 200. %. In this case, the C point of the color separation table of the medium A is first increased by 20% and changed to 200%. Accordingly, the C value of the frame line (in this case, any one of Bk-C, WC, CB, and CG) set in step S605 is linearly increased by 20%, and this is increased to media B. The value of the frame line of the color separation table.

  In step S608, the nonlinear correction coefficient strength of each color is determined in accordance with the priority order of each evaluation item set in step S603. The non-linear correction coefficient strength is used at the time of non-linear correction for each ink color of main colors (C, M, Y, K), light colors (Lc, Lm, Lk1, Lk2), and adjacent colors (R, G, B). Each of which is E1, E2, E3. For example, when “granularity priority” is set as the evaluation item, the nonlinear correction coefficient strength is set to E1 = 1, E2 = 3, and E3 = 1 in order to effectively use light ink. For example, when “color gamut priority” is set as the evaluation item, the nonlinear correction coefficient strength is set to E1 = 3, E2 = 1, and E3 = 2 in order to effectively use the main color ink.

  In step S609, the main color is corrected using the non-linear correction coefficient strength E1. In step S610, the light color is corrected using the nonlinear correction coefficient strength E2. In step S611, the adjacent color is corrected using the nonlinear correction coefficient strength E3. It should be noted that a known correction method using parameters that enable nonlinear correction can be applied to the correction of ink color data using the nonlinear intensity coefficients E1, E2, and E3 in the present embodiment.

  In step S612, it is determined whether the total ink amount for each lattice point on the frame line being processed has reached the value indicated by the total color material amount restriction information. There are various possible determination methods. For example, in consideration of an intensity update method in step S613, which will be described later, the maximum value of the ink amount based on the current correction result does not exceed the value indicated by the total color material amount restriction information. What is necessary is just to determine whether it becomes a value.

  If each value on the frame line has not reached the value indicated by the total color material amount restriction information, that is, there is still room for correction, it is updated in step S613 to increase the nonlinear correction coefficient strengths E1, E2, and E3. Then, the corrections in steps S609 to S611 are performed again. As a method for updating the nonlinear correction coefficient strength in step S613, for example, one may be added to each coefficient strength, but the present invention is not limited to this example. By such a determination loop in step S612, all the values on the frame line are controlled as close to the total color material amount restriction information as possible, and the set total color material amount is realized to the maximum. A color separation table for media B can be created.

  In step S614, it is determined whether or not the processing has been completed for all 19 frame lines in the color separation table for media B. If the processing has not been completed, the process returns to step S605 to process the next frame line. .

Optimization of Color Separation Table Frame Line Hereinafter, the color separation table optimization processing based on color prediction in step S504 in FIG. 5 will be described in detail with reference to the flowchart in FIG.

  The color separation table before optimization generated in step S503 strictly observes the total color material amount of the medium B, but does not consider the color that is actually expressed by the corrected ink combination. Therefore, when printing is performed using the color separation table as it is, color misregistration and pseudo contour may occur. In order to suppress the occurrence of such color shift and pseudo contour, the following optimization process is performed in the present embodiment.

  First, in step S703, the Lab value of the medium A is calculated by color prediction such as cellular Neugebauer and set as a target. Specifically, a CMYK value that maximizes the ink color gamut is obtained for the medium A, and this is converted into a Lab value. This process is performed based on a color reproduction characteristic table holding the primary Lab value of the medium A.

  In step S704, the color gamut in the medium B is predicted. Specifically, the CMYK value that maximizes the ink color gamut is obtained for media B, and this is converted to a Lab value. This process is performed based on a color reproduction characteristic table holding the primary Lab value of the medium B.

  Note that the processing order of steps S703 and S704 may be switched.

  In the present embodiment, it has been described that the color reproduction characteristic table corresponding to each medium is referred to in steps S703 and S704 described above. The present embodiment is characterized in that patches referred to in order to appropriately create this color reproduction characteristic table are more appropriately created. The color reproduction characteristic table creation process will be described later.

  In step S705, the Lab value of the maximum color gamut of media B predicted in step S704 is compared with the target Lab value calculated in step S703, and the comparison result is reflected to optimize the frame line in the color separation table. Turn into. Details of this optimization method will be described later. Since this optimization is performed as a Lab value, a CMYK value corresponding to the optimization result is obtained by a known search method.

  In step S706, a smoothing process is performed on the frame lines of the color separation table to further improve the gradation. Specifically, the black gradation in the Bk-W gray line is retained, and for the other color materials, the gradation change is monotonously increased and monotonously reduced to eliminate a singular point, Connect it smoothly.

Color Reproduction Characteristic Table Creation Processing Hereinafter, the color reproduction characteristic table creation processing held for each medium in the present embodiment will be described with reference to the flowchart of FIG. Here, the color reproduction characteristic table according to the present embodiment includes reproducible color gamut information including, for example, colorimetric values of gradation patches based on a single ink color or mixed color patches based on all color inks on a medium.

  First, in step S801, colorimetric data of an original single color gradation patch is input. Here, the original single color gradation patch is composed of a number of patches that can sufficiently grasp the color reproduction characteristics of the single color on the medium, and is printed and measured before starting this processing. To do. At this time, various parameters such as the total color material amount restriction information of the medium and the number of grids of the ink space in the color reproduction table to be created are also input.

  Next, in step S802, the first feature of the present embodiment, which is the single color gradation patch data, is optimized. Details of the optimization processing will be described later.

  Next, in step S803, after all primaries are generated, patches are generated only for primaries that can be printed because the total color material amount is within the total color material amount limit.

  In step S804, the number of printed patches is input. In step S805, it is determined whether the number of patches generated in step S803 is larger than the number of printed sheets input in step S804. When there are many, it progresses to step S806, and after performing the reduction process of the number of patches which is the 2nd feature of this embodiment, it progresses to step S807. Details of the patch reduction processing will be described later. On the other hand, if the number of patches is equal to or smaller than the number of prints, the process proceeds to step S807, and the patch generated in step S803 is printed out.

  In step S808, the color of the printed patch is measured, and in step S809, the color measurement result is input. In step S810, the colorimetric value is used to estimate a primary spectral value that cannot be printed because the total color material amount is larger than the total color material amount limit. As a result, the colorimetric value, that is, the spectral value is obtained for the primary of all grid points, and the color reproduction characteristic table is completed.

  In the present embodiment, by using the color reproduction characteristic table created in this way, color prediction can be performed for any point in the color space including the primary. Specifically, when a signal value of a point to be predicted is input, by performing color prediction by a known cellular Neugebauer process based on the colorimetric values of the primaries around the point in the color reproduction characteristic table, The spectrum value of the point can be output.

Monochromatic Tone Patch Data Optimization Processing Hereinafter, monochromatic tone patch data optimization processing, which is the first feature of the present embodiment, will be described. In the present embodiment, the single-color gradation patch data is optimized according to the nonlinearity of the coloring characteristics of the color material.

  First, prior to describing the optimization of the single color gradation according to the present embodiment, a method for generating single-color gradation patch data by equal assignment in the color space, which has been conventionally performed, will be described.

  FIG. 9 is a diagram showing an example in which a color material space of two colors C and M is equally divided into five grids as usual. W to C are divided by 0, 64, 128, 192, and 255. Similarly, W to M are divided by 0, 64, 128, 192, and 255. That is, there are 25 primaries (uniform primaries) in the color material space of two colors.

  FIG. 10 is a diagram illustrating an example in which the color measurement result of the printed matter of the uniform primary single color patch illustrated in FIG. 9 is plotted in the a * b * space indicating the color development characteristics of each color. In the figure, an example in which uniform primary is set by equally dividing 5 grids for the Y color as well as C and M, and the single color patch is measured is shown.

  In FIG. 10, lines 301, 302, and 303 are color development characteristics (tone trajectories) of the C color material, the M color material, and the Y color material, respectively. It is assumed that these lines are acquired in advance based on a larger number of predetermined monochrome gradation patches (original gradation patches) before setting the monochrome gradation patches in the present embodiment.

  Reference numerals 304, 305, 306, and 307 respectively indicate the colorimetric results of the C single color patch printed with the signal values of 64, 128, 192, and 255 on the C color material. Reference numerals 308, 309, 310, and 311 respectively indicate the color measurement results of the M single-color patch printed with the signal values of 64, 128, 192, and 255 in the M color material. Reference numerals 312, 313, 314, and 315 respectively indicate the color measurement results of the Y single color patch printed with the signal values of 64, 128, 192, and 255 in the Y color material. According to the figure, it can be seen that the color development characteristics of the C color material and the M color material indicated by the lines 301 and 302 exhibit nonlinearity.

  Next, a non-uniform primary of monochromatic gradation obtained as a result of performing optimization according to the present embodiment on the above-described conventional uniform primary will be described.

  FIG. 11 shows an example in which a color material space of two colors C and M is divided into five grids optimized as described later in the present embodiment. In this example, W to C are divided by 0, 70, 140, 210, and 255, and W to M are divided by 0, 80, 160, 240, and 255. That is, there are 25 primaries (non-uniform primaries) in the color material space of two colors, but the primaries are evenly arranged in the color space, unlike the uniform primary shown in FIG. 9 described above. is not.

  FIG. 12 is a diagram illustrating an example in which the colorimetric result of the printed matter is plotted in the a * b * space for the non-uniform primary single color patch shown in FIG. In the same figure, for Y color, an equal primary is set by equal division of 5 grids as in FIG. 10, and the color of the single color patch is measured.

  In FIG. 12, lines 121, 122, and 123 are monochromatic characteristics (gradation trajectories) based on original gradation patches of C color material, M color material, and Y color material, respectively, as in FIG. Reference numerals 124, 125, 126, and 127 indicate the colorimetric results of the C single-color patches printed with the signal values of 70, 1140, 210, and 255 in the C color material, respectively. Reference numerals 128, 129, 130, and 131 respectively indicate the color measurement results of the M single-color patch printed with the signal values of 80, 160, 240, and 255 in the M color material. Reference numerals 132, 133, 134, and 135 respectively indicate the color measurement results of the Y single-color patch printed with the signal values of 64, 128, 192, and 255 in the Y color material.

  In the present embodiment, a color material whose color development characteristics exhibit nonlinearity is an adjustment target. That is, in the example of FIG. 12, the monochromatic gradation of the color material is adjusted so as to consider the non-linearity with respect to the C color and the M color. Specifically, the inflection point of the gradation trajectory is detected by connecting the W point and the primary of the 100% single color patch with a straight line in the Lab space and calculating the differentiation of the monochromatic gradation trajectory and the straight line. The primary is placed at the inflection point. Then, using the primary arranged at the inflection point as a reference, the primary is equally arranged for the gradation locus between the primary and the W point.

  For example, with respect to the line 121 indicating the gradation locus of the C color material in FIG. 12, the C single color patch 127 having the signal value 255 and the W point that is the center of the a * b * space are connected by a straight line. An inflection point is obtained based on the derivative value of. As a result of arranging the primary for the inflection point, in this example, the primary corresponds to the C single color patch 126 of the signal value 210. Then, between the C single color patch 126 and the W point in the line 121, the C single color patches of 125 and 124 are obtained as signal values 140 and 70 corresponding to the remaining three grids, respectively. It is done.

  As described above, the inflection points of the C and M lines 121 and 122 in FIG. 12 are detected and set as primary, so that the monochrome gradation in the present embodiment is optimized.

  FIG. 13 is a flowchart showing the optimization process of the monochrome gradation patch in step S802 described above. That is, the grid position for generating a single color patch is optimized.

  First, in step S131, a color measurement result of an original gradation patch that forms a monochrome gradation locus is input. Then, the processes in steps S132 to S135 loop with the number of monochrome gradations in the original gradation patch, that is, the number of original patches. Hereinafter, the processing in the loop will be described.

  In step S133, the curvature is calculated by the above-described differentiation operation for each point corresponding to the original gradation patch. In step S134, if the curvature is maximum, this is set as an inflection point. In other words, the original gradation patch position having the maximum curvature is detected as an inflection point by the loop.

  In step S136, a single color division point (primary) on the color material space is arranged at the inflection point, and the other primaries are arranged by equal division from the inflection point.

Patch reduction processing The patch reduction processing, which is the second feature of this embodiment, will be described below. FIG. 14 is a flowchart showing details of the patch reduction process in step S806 of FIG.

  First, in step S1401, various parameters are input. Here, the number of grids, the number of inks, and the upper limit number of patches as patch number limit information are input as parameters. Further, an input such as an OPG (OutPut Gamma Generators) table and an AMT (AMounT) table for calculating the driving amount is also performed. For example, if you want to limit the number of patches used when creating the color reproduction characteristic table to two A4 size sheets for printing and color measurement, set the maximum number of patches on the two A4 size sheets. To do. Note that the input of the upper limit number of patches is performed by a user interface (not shown).

  In step S1402, the number of inks that need to be adjusted is input. In step S1403, the ink color is input. In the present embodiment, the ink to be adjusted is an ink having a low linearity of the color development characteristic, that is, particularly non-linearity. For example, in the example of FIG. 12 described above, in order to adjust the non-linearity with respect to the C and M colors, the number of inks to be adjusted is input as 2 in step S1402, and the ink color to be adjusted is set to C in step S1403. , M.

  In step S1404, a parameter tmp for calculating a color material ratio to be deleted, which will be described later, is initialized to 1.0. In step S1405, a color material ratio x to be deleted of the print primary is calculated. Here, as shown in FIG. 15, x is a parameter indicating the total formula material amount of the color material for the print primary deleted in each section (CM section in FIG. 15), and is calculated according to the following formula. That is, when the total amount of formula material to be driven is larger than x% of the limit value, it is determined that the primary should be deleted from the printing target.

x = 1.0− (tmp × 0.1)
In step S1406, a variable Count that is a counter of the number of processed grids is initialized to zero.

  In step S1407, the primary data of NUM [ink color] [n] [i] is sorted in order of the total color material amount. Here, n is an index indicating a section type, and i is an index indicating a primary in the section n.

  In step S1408, it is determined whether or not the total color material amount of NUM [ink color] [n] [i] is larger than x% of the limit. If so, the process proceeds to step S1409 to delete the primary data. If it is smaller, the process proceeds to step S1410.

  In step S1410, it is determined whether the number of patches is larger than the upper limit even if the NUM [ink color] [n] [i] primary is deleted in step S1409. If the number of patches is large, the process proceeds to step S1411 and the deletion process is continued. However, if the number of patches is equal to or less than the upper limit, the patch deletion process is terminated as it is.

In step S1411, Count is compared with the number of grid adjustment target inks (the number of adjustment target inks is ² and 4 ^{2 in} the case of 4 grids), that is, the total number of grids. Therefore, if Count is smaller than the total number of grids, it is determined that there remains a processing target grid, and Count is incremented in step S1412, and the process returns to step S1407. On the other hand, when Count reaches the total number of grids, the process has been completed for all the grids although the upper limit number of patches has been exceeded, the process proceeds to step S1413.

  In step S1413, if the value of tmp is 10 or less, the process proceeds to step S1414 to perform further deletion processing, and tmp is incremented to increase the color material ratio to be deleted, and the process returns to step S1405. On the other hand, if tmp is greater than 10, the deletion target color material rate x is 0 or less, so that no further deletion processing is possible, the process proceeds to step S1415, and an error message is output.

  Note that the processing in steps S1408 to S1412 described above loops in section n while the number of patches remaining after deletion is greater than the upper limit and the processing target grid remains. Therefore, at the end of the loop, the primary data is deleted in descending order of the total color material amount in the section. This loop processing is further performed sequentially for each ink color to be adjusted, but this loop control is not shown and detailed description is omitted.

  The deletion order of primary corresponds to the arrangement order after the sorting in step S1407. That is, the priority order of deleted primaries is, as indicated by the circled numbers in FIG. 15, in the order close to the limit of the total color material amount, excluding the frame line on the color space, that is, in the order of the largest total color material amount.

  In the deletion step of step S1409, it may be possible to refer to the flag in the subsequent color prediction process by setting a predetermined flag or the like indicating that the primary has been deleted. It is also possible to count the number of deleted primaries by sequentially decrementing a predetermined counter.

  As described above, according to the present embodiment, by creating a patch in consideration of the nonlinearity of the tone characteristics of a predetermined color material for a predetermined medium, the color reproduction characteristic table of the color material can be further obtained. Can be created appropriately.

  Furthermore, since it is possible to preferentially delete patches with a large total colorant amount based on the upper limit number of patches, it is possible to limit the number of media on which patches are printed without degrading color prediction accuracy.

  Thus, an optimum color separation table can be created by performing color prediction based on the optimum color reproduction characteristic table for the medium.

  For example, when the second color separation table optimal for the second medium is automatically created using the first color separation table for the existing first medium, the first and second color reproduction characteristics are respectively generated. Optimization can be performed by color prediction based on information (color reproduction characteristic table).

  In the present embodiment, the Lab space is used as the color space. However, other color spaces may be used.

  Moreover, although the example which performs the color prediction process accompanying color separation table preparation in the computer 202 was shown, you may perform this by hardware, such as a color prediction engine.

<Other embodiments>
The present invention can take the form of, for example, a system, apparatus, method, program, or storage medium (recording medium). Specifically, the present invention may be applied to a system composed of a plurality of devices (for example, a host computer, an interface device, an imaging device, a web application, etc.), or may be applied to a device composed of a single device. good.

  The present invention also provides a software program that implements the functions of the above-described embodiments directly or remotely to a system or apparatus, and the system or apparatus computer reads out and executes the supplied program code. Achieved. The program in this case is a computer-readable program corresponding to the flowchart shown in the drawing in the embodiment.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, or the like.

  Recording media for supplying the program include the following media. For example, floppy disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD- R).

  As a program supply method, the following method is also possible. That is, the browser of the client computer is connected to a homepage on the Internet, and the computer program itself (or a compressed file including an automatic installation function) of the present invention is downloaded to a recording medium such as a hard disk. It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. It is also possible to make it. That is, the user can execute the encrypted program by using the key information and install it on the computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Furthermore, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, and then executed, so that the program of the above-described embodiment can be obtained. Function is realized. That is, based on the instructions of the program, the CPU provided in the function expansion board or function expansion unit can perform part or all of the actual processing.

It is a figure which shows the image output process in the color printer of one Embodiment which concerns on this invention. It is a figure which shows the system configuration | structure in this embodiment. It is a figure which shows the structure of the ink color separation table in this embodiment. It is a figure which shows the cube on RGB color space as a color separation table in this embodiment. It is a flowchart which shows the automatic creation process of the color separation table in this embodiment. It is a flowchart which shows the automatic creation process of the frame line of the color separation table in this embodiment. It is a flowchart which shows the optimization process of the frame line of the color separation table in this embodiment. It is a flowchart which shows the color reproduction characteristic table creation process in this embodiment. It is a figure which shows a common equal primary example. It is a * b * top view of a general equal primary. It is a figure which shows the nonuniform primary example in this embodiment. It is a * b * top view of a non-uniform primary in this embodiment. It is a flowchart which shows the optimization process of the monochrome grid position in this embodiment. It is a flowchart which shows the patch reduction process in this embodiment. It is a figure which shows the example of a deletion order of the primary in this embodiment. It is a flowchart which shows the preparation processing of the conventional color reproduction characteristic table.

Claims (10)

A color processing method for creating color reproduction characteristic information of a medium used when creating a color separation table for separating image data into data for a plurality of color materials,
A grid point acquisition step of acquiring grid points obtained by dividing the color space corresponding to the plurality of color materials into a grid pattern;
An input step of inputting a colorimetric value obtained by printing a patch of the grid points on the medium;
In the grid point acquisition step,
Obtaining a monochrome gradation characteristic for obtaining a monochrome gradation characteristic for each color material for the medium;
An inflection point detecting step for detecting an inflection point in the monochrome gradation characteristic;
A grid point placement step of placing one of the grid points at the inflection point;
A color processing method characterized by comprising: Obtaining restriction information for obtaining restriction information on the total amount of color material for the medium;
A patch generation step of generating a patch for grid points whose total colorant amount is within the limit indicated by the limit information;
The method further comprises an estimation step of estimating a colorimetric value of a grid point having a total color material amount larger than the limit indicated by the restriction information based on the colorimetric value input in the input step. The color processing method according to 1. In the grid point acquisition step,
The grid point placement step further includes another grid point placement step of placing other grid points equally with reference to the grid point placed at the inflection point. Color processing method. Furthermore, a patch number limit acquisition step for acquiring patch number limit information;
A reduction step of reducing the patches generated in the patch generation step based on the patch number restriction information;
The color processing method according to claim 2, further comprising:   5. The color processing method according to claim 4, wherein in the reduction step, the color processing method is preferentially deleted from patches corresponding to lattice points having a large total color material amount. A step of obtaining a first color separation table for obtaining a first color separation table for the first medium;
Obtaining restriction information for obtaining restriction information on the total amount of color material for the second medium;
A second color separation table generating step for generating a second color separation table for the second medium based on the first color separation table and the restriction information of the second medium;
Acquiring the color reproduction characteristic information for the first medium and the color reproduction characteristic for obtaining the color reproduction characteristic information for the second medium;
A correction step of correcting the second color separation table by color prediction based on the color reproduction characteristic information for the first and second media;
The color processing method according to claim 1, further comprising:   The color processing method according to claim 6, wherein the first color separation table is manually created in advance.   An image forming apparatus for performing image formation on the second medium using a plurality of color materials using the second color separation table created by the color processing method according to claim 6 or 7. .   A computer-readable program that controls a computer to execute the color processing method according to any one of claims 1 to 7 when the computer reads and executes the computer.   A computer-readable recording medium, wherein the program according to claim 9 is recorded.

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